The Nigerian army has been accused of committing crimes against humanity in a recent clash with Islamic terrorist organization Boko Haram that left 600 people dead, Amnesty International said in a report, noting that the violence and death toll in the conflict has escalated greatly in 2014.

"The scale of atrocities carried out by Boko Haram is truly shocking, creating a climate of fear and insecurity. But this cannot be used to justify the brutality of the response that is clearly being meted out by the Nigerian security forces," said Netsanet Belay, Research and Advocacy director for Africa at Amnesty International, in a statement Monday.

"The summary killing of these detainees amount to extrajudicial executions and are crimes under international law. These killings follow an entrenched pattern of deaths in custody of detainees held in relation to the situation in the northeast."

The human rights group noted that following a March 14 attack by Boko Haram gunmen at the Giwa military barracks in Maiduguri, Borno, who managed to free hundreds of detainees, Nigeria's military regained control and killed over 600 people, many reportedly unarmed recaptured detainees.

BBC News noted that the army has not yet responded to the report, but has previously denied allegations of abuse.

Amnesty estimates that at least 1,500 people have lost their lives in 2014 so far in the conflict between Boko Haram, an extremist Islamic group, and the Nigerian government. The Islamic group has killed thousands of Christians and civilians in the past several years in its mission to bring down the government, drive out followers of Christ, and establish Islamic rule in the African nation.

"More than 1,500 deaths in three months indicate an alarming deterioration in the situation," Amnesty said.

"The international community cannot continue to look the other way in the face of extrajudicial executions, attacks on civilians and other crimes under international law being committed on a mass scale. Civilians are paying a heavy price as the cycle of violations and reprisals gather momentum."

As for Nigeria's army alleged killing of 600 people, Belay argued that human rights abuses cannot be excused even in the face of Boko Haram's crimes. Amnesty also shared first-hand witness accounts of the killings.

"The international community, and in particular the African Commission on Human and People's Rights and the UN Human Rights Council, must, as a matter of urgency, ensure that a thorough, impartial and transparent investigation is conducted into these allegations of war crimes and crimes against humanity in Nigeria," the advocacy director offered.

"The escalation of violence in north-eastern Nigeria in 2014 has developed into a situation of non-international armed conflict in which all parties are violating international humanitarian law. We urge the international community to ensure prompt, independent investigations into acts that may constitute war crimes and crimes against humanity."

Earlier in March, the Christian Association of Nigerian-Americans called on the federal government to offer more support to the army and to the thousands of refugees fleeing the country to escape Boko Haram's attacks.

"Boko Haram is making nonsense of the claim of the Nigerian government to be in charge of the situation, and we want the federal government to redouble its security effort to contain the situation again," said CANAN Executive Director Pastor Laolu Akande.